LIF and neoplasm: Importantly, it has been demonstrated that Il-6 [33,34], Il-11 [35], Osm [29], Lif [36,37], and Cntf [38,39] are expressed by osteoblast-lineage cells and that Ct-1 is expressed by osteoclasts [30], suggesting that tumor cells in the bone marrow will encounter these signals in the physiological bone marrow microenvironment (Figure 2).